Wikipedia
Ghestem
In the game of bridge, Ghestem is a conventional overcall structure, using 2NT, 3, and the (non-jump) cuebid over an opposing opening at the one level to denote two-suited hands in two of the remaining three suits.
This convention was devised by the French bridge and checkers player Pierre Ghestem.
When playing Ghestem, after an opposing one-level opening, the three overcalls mentioned denote the three possible two-suited hands in the suits excluding the opened suit:
2NT : shows the two lowest-ranking unbid suits 3 : shows the two highest-ranking unbid suits Cuebid : shows the top- and bottom-ranking unbid suits